This invention relates to countercurrent flow heat exchange and mass transfer apparatus, and more particularly to countercurrent flow desorbers and absorbers for use in open cycle refrigeration and thermal boosting systems.
In many instances requiring refrigeration, rather than utilizing a mechanical refrigeration cycle, an absorption refrigeration cycle is used. Absorption refrigeration cycles are heat operated cycles in which a secondary fluid, the absorbent, is employed to absorb a primary fluid, the refrigerant, which has been vaporized in an evaporator. A basic absorption refrigeration cycle has five components--a desorber (commonly termed generator), a condenser, an evaporator, an absorber, and a solution pump.
In operation, heat is supplied to the desorber to boil off relatively high pressure refrigerant vapor. The vapor passes to the condenser where the refrigerant is condensed to provide a liquid at a relatively high pressure. The refrigerant then passes to an evaporator where it is flashed to form liquid and vapor fractions at a low pressure. Heat from a low temperature source is transferred into the system at this point providing the refrigeration effect as it vaporizes the liquid refrigerant. This vapor is then passed to an absorber where at least a portion of it is absorbed by an absorbent-refrigerant solution sprayed over the absorber surface. The solution pump pressurizes the collected absorbent-refrigerant solution and transfers it to the desorber to complete the cycle.
In thermal boosting systems utilizing a Rankine cycle evaporator coupled with a solution heat pump such as those disclosed by Bearint in copending U.S. application Ser. No. 139,051, now abandoned, filed Apr. 10, 1980, and commonly assigned, heat is supplied to an evaporator to produce a source of relatively high pressure refrigerant vapor. The vapor is then passed to the absorber where at least a portion of it is absorbed by an absorbent-refrigerant solution sprayed over it. The heats of condensation and solution released by the refrigerant supply the temperature boost. The absorbent-refrigerant solution is then passed to a desorber where refrigerant is vaporized at a relatively low pressure. The refrigerant vapor is then condensed and pumped to the evaporator to complete the cycle.
In both the refrigeration and thermal boosting systems, not only must efficient heat transfer occur in the absorber and desorber sections but also efficient mass transfer of refrigerant into and out of solution must occur. In prior refrigeration systems, the desorber section of the system consisted of a chamber having heat exchange tubes immersed in a pool of absorbent-refrigerant solution. Heat transfer was limited by the surface area of the tubes, residence time of the solution, and back mixing which occurred as new solution was fed into the chamber and as convective recirculation occurred in the pool. Mass transfer was similarly limited by the relatively small surface area of the pool of solution and lower temperature attainable because of inadequate heat transfer.
The absorber section of previous refrigeration systems also suffered from deficiencies in heat and mass transfer. Both heat and mass transfer were limited by relatively short residence times of the solution in the absorption chamber.
Accordingly, the need exists in the art for absorber and desorber apparatuses having improved heat and mass transfer characteristics.